Since organophosphorus insecticides are biochemically reactive chemicals, they can form various stable covalent bonds with macromolecules (proteins and nucleic acids) of the cell. In view of the demonstrated side effects (teratogenicity and delayed neurotoxicity) of many common organophosphates, potential alterations of macromolecules of vital functions by organophosphates will be studied as a possible basis of health hazards. Using labelled DFP,paraoxon, parathion and related organophosphates, covalent bond formations with various tissues, subcellular coponents and selected proteins and nucleic acids of physiological importance will be studied by biochemical and histological techniques. Rats and chicken eggs will usually serve as experimental animals. Study of dialkylphos-phorylation will be emphasized, but alkylation and sulfur binding will also be examined. Factors that influence the macromolecular interactions will be investigated in relation to biotransformation of organophosphates.